Mass transfer properties of osmotic solutions. I. Water activity and osmotic pressure

Abstract

In this review paper data on water activity, solute activity and osmotic pressure of”; binary and multi‐component osmotic solutions are provided. The Characteristics of the osmotic solutions are needed for the optimization of mass transfer during osmotic process, and for the improvement of final product quality. The vant Hoff equation and Gibbs Duhem theorem are commonly used to estimate osmotic pressure and solute activity. Water activities can be easily estimated through experimental determination of the freezing point depression. The possibilities of the group contribution models such as the Analytical Solution of Groups (ASOG) approach are also explored. The future needs especially in the case of multicomponent solutions consisting of electrolyte and non‐electrolyte mixtures are pointed out.     

The prediction of water activity of some supersaturated non-electrolyte aqueous binary solutions from ternary data

Binary data are required for prediction of the water activities of multicomponent aqueous solutions by various methods. At high concentrations, these methods would need binary data beyond the solubility limits of individual solutes. Such supersaturated data are usually lacking or very difficult to determine experimentally. The Zdanovskii–Stokes–Robinson equation, which has been shown to be a reliable and accurate method for predicting the water activity of complex solutions, may be applied in reverse to calculate the water activities of supersaturated binary solutions from ternary data. Hitherto unpublished supersaturated binary a _w data of mannitol, sucrose and urea obtained using this method as well as polynomials for their prediction are presented in this paper.     

Drying characteristics and sorption isotherms of silverside fish (Atherina)

The aim of this work was to report drying characteristics and sorption isotherms of silverside fish. The sorption isotherm was determined at four temperature levels 40, 50, 60 and 70 °C and at water activities, ranging from 0.058 to 0.89, using the static gravimetric method. Five sorption models were fitted with the desorption data generated from the gravimetric method. It was found that the Peleg model suitably represents the sorption experimental data in the mentioned investigated ranges of temperature and water activities. Sorption isosteric heat was determined from sorption data using the Clausius–Clapeyron equation. The relationship between the net isosteric heat of sorption and the moisture content was best expressed by the Tsami’s equation. The drying characteristic curve and the drying rate expression of silverside fish have been established from experimental convective drying kinetics.     

Computational fluid dynamics modeling of mass transfer for aroma compounds recovery from aqueous solutions by hydrophobic pervaporation

In this work, a mass transfer study on aroma compound recovery by pervaporation process was performed using a model based on solution–diffusion theory. CFD method was employed to solve the governing mass transfer equations by considering the flux coupling. Concentration profiles of penetrants inside the membrane as well as permeation flux and aroma permeate concentration through the membrane were determined. The modeling results were validated by the experimental data obtained for pervaporative recovery of isopentyl acetate and n-hexanol from their binary aqueous solutions with composite PDMS membrane. The influence of key operating parameters such as feed aroma concentration and temperature on the flux and permeate concentration was also investigated theoretically and experimentally. The results showed that the aroma permeate concentration as well as the total and partial fluxes increased with an increase in the feed aroma content and feed temperature. The predicted results were in good agreement with experimental data.     

Solubility of disodium 5′-guanylate heptahydrate in aqueous methanol mixtures

The solubility of disodium 5′-guanylate heptahydrate (5′-GMPNa₂) in binary aqueous methanol solvent mixtures with the temperature ranging from 278.15 to 323.15 K was measured by a dynamic method with a laser monitoring observation technique. The solubility data were correlated with the Combined Nearly Ideal Binary Solvent/Redlich–Kister (CNIBS/R–K) model and the modified Jouyban–Acree model, respectively. For the ten groups of data studied, the CNIBS/R–K model was found to provide a more accurate mathematical representation of the experimental data, while the modified Jouyban–Acree model containing provisions for correlating both the solvent composition and temperature.     

Rheology of supersaturated sucrose solutions

Sucrose solutions, with concentrations near or superior to saturation, present high potentialities for the candy and pastry industries. Creep measurements under small stresses were done to obtain the rheological properties of highly concentrated sucrose solutions, since such solutions could be in a metastable state and tend to crystallise. The viscosities of these solutions, from 70.0% to 85.2% (w/w), were determined experimentally at different temperatures, from 0 to 90 °C. The temperature dependence of viscosity was studied using experimental and published data for, respectively, high and low concentrations (<70% (w/w)). Results showed that the Arrhenius model describes better the temperature dependence of viscosity for concentrations under saturation and in the high concentration regime the WLF model had a better predicting ability. The effect of concentration on viscosity was observed and included in the Arrhenius and WLF models’ parameters. The proposed models were able to successfully describe the data in the corresponding concentration range. These results can be used in predicting the viscosities of syrups for either process design or new products formulation.     

Kinematic viscosity and water activity of aqueous solutions of glycerol and sodium chloride

During osmotic dehydration, a removal of water from foodstuffs is achieved with a decrease in the water activity of the food sample. This dehydration process involves the utilization of highly concentrated solutions with one or several solutes that increase considerably the viscosity of the liquid phase. This property is fundamental in the studies of mass and momentum transfer processes. Glycerol and sodium chloride are studied as systems employed in this type of process due to the advantages for the final dehydrated product. Kinematic viscosities of binary and ternary aqueous solutions of these solutes were measured at various concentrations (from 0 to up 5.0 mol kg^–1) and temperatures (from 20 up to 50 °C). Water activities for each indicated solution at 25 °C are also reported. Experimental data for both physical properties were simultaneously correlated with concentration and temperature for binary and ternary solutions with a suitable accuracy. Additionally, relationships between kinematic viscosities and water activities were established.     

Kinetics of Thiamin and Riboflavin Loss in Pasta as a Function of Constant and Variable Storage Conditions

The stability of thiamin and riboflavin in enriched pasta humidified to different water activities was measured at 25, 35, 45, and 55°C for periods of up to 1 yr. Riboflavin was shown to be extremely stable (dark reaction) whereas thiamin losses were significant. Thiamin loss increased with temperature (Q₁₀ of 4.5) and water activity. Predictions of thiamin loss for a square wave temperature fluctuation using steady state data were compared to actual losses found in storage for pasta held at equal alternating times at 25/45 and 25/55°C. The Hicks-Schwimmer-Labuza model provided an adequate method for predicting both the amount of loss and the effective temperature from steady state data.     

Sorption isotherms and isosteric heat of sorption for grapes, apricots, apples and potatoes

Moisture sorption isotherms of grapes, apricots, apples and potatoes were determined at 30°C, 45°C, and 60°C using the standard, static-gravimetric method. Six two-parameter and five three-parameter sorption models were tested to fit the experimental data. A nonlinear regression analysis method was used to evaluate the constants of the sorption equations. The Halsey equation gave the best fit to the experimental sorption data for all materials tested over the range of temperatures and water activities investigated. The GAB model gave also the closest fit to the sorption data for potatoes and grapes. The agreement between experimental and predicted values of these models was found to be satisfactory. The isosteric heat of desorption and adsorption of water determined from the equilibrium data using the Clausius-Clapeyron equation.     

Osmotic dehydration of apples in sugar/salt solutions: Concentration profiles and effective diffusion coefficients

Apples (Fuji variety) were treated in aqueous sucrose (50% w/w) and salt (NaCl, 10% w/w) solutions for 2, 4 and 8 h (27 °C). Concentration profiles were determined as a function of the distance, considering the unidirectional and normal diffusion to the exposed face of the immersed fruit. The density, water, sugar and salt contents were determined for each piece of apple. A mathematical model was fitted to the experimental data for the water, sucrose and salt contents. A numerical method of finite differences allowed for the calculation of the effective diffusion coefficients as a function of concentration, using the material coordinates to consider tissue shrinkage. The coefficients were obtained by simultaneously integrating the three differential equations (for water, sucrose and salt). The behavior of the apple cellular tissue was also studied using light microscopy techniques to obtain images of the osmotically treated pieces.     

油橄榄叶醇提取物对D-半乳糖胺/脂多糖致小鼠急性肝损伤的保护作用及其作用机制

研究油橄榄叶醇提取物(OLME)对D-半乳糖胺/脂多糖诱导小鼠肝损伤的保护作用。昆明种小鼠按体质量随机分为6组,即空白对照组、模型对照组、阳性对照组(联苯双酯200 mg/kg·d)、OLME低、中、高剂量组(200、400、800 mg/kg·d)。每天给药1次,连续给药14 d,末次给药1 h后,除正常组外其余各组用600 mg/kg·BW D-半乳糖胺和40 μg·kg-1脂多糖腹腔注射以复制小鼠急性肝损伤模型,末次给药12 h后,摘眼球取血,取材。用生化法测定小鼠血清中谷氨酸转氨酶(ALT)和天冬氨酸转氨酶(AST)活性,用试剂盒测定各组小鼠肝匀浆中超氧化物歧化酶(SOD)和谷胱甘肽过氧化物酶(GSH-Px)活性、丙二醛(MDA)含量、肿瘤坏死因子-α(TNF-α)、白细胞介素-1β(IL-1β)和白细胞介素-6(IL-6)等炎性因子的表达水平以及半胱氨酸天冬氨酸蛋白酶-3(Caspase-3)和半胱氨酸天冬氨酸蛋白酶-8(Caspase-8)活性。与模型组比较,OLME中高剂量组小鼠血清中ALT和AST活力显著降低(p<0.05),肝组织中MDA、TNF-α、IL-1β和IL-6含量显著降低而SOD活力显著升高(p<0.05),但OLME对GSH-Px改善作用不明显,仅OLME高剂量有一定效果;OLME低、中、高剂量均能显著降低caspase-3和caspase-8活性(p<0.05)。OLME对D-半乳糖胺/脂多糖诱导的小鼠急性肝损伤具有较好的保护作用。     

Fractionation of fish oil with supercritical carbon dioxide

In order to verify the possibility of using supercritical CO₂ (SC-CO₂) to concentrate polyunsaturated ω−3 fatty acids in the form of natural fish oil, experimental phase equilibrium data were measured for a CO₂ – fish oil system. Phase equilibrium was measured at temperatures from 301 to 323 K and pressures from 7.8 to 29.4 MPa, using the dynamic method. The oil solubility and fatty acid composition of the extracts were measured and these data used to verify CO₂ selectivity. The best operational conditions to fractionate the oil were 7.8 MPa and 301.15 K, although in all the conditions analyzed, eicosapentaenoic acid (EPA) could not be fractionalized. The equilibrium for a mixture of 50% fish oil and 50% babassu (Attalea funifera) fat was measured in order to understand how the fatty acid composition influenced the fractionation. It was observed that the solubility of the mixture was an average of the individual solubility values, and the composition of the extracts could be calculated from the individual solubility of each component.     

On water dynamics and germination time of mold spores in concentrated sugar and polyol solutions

The relative effect of concentrated solutions of selected glass formers on germination time at 28 °C of mold spores of Aspergillus flavus, A. niger and Eurotium herbariorum was determined. Solutes included glucose, fructose, mannose, glycerol, sucrose, maltose and propylene glycol. The effect of fructose concentration on the germination time of A. parasitions was also studied. The results did not agree with previous literature experimental data used to support a ‘water dynamics’ approach of microbial stabilization in concentrated sugar and polyol solutions.     

The evaluation of water activity in aqueous solutions from freezing point depression

The water activity of various non-electrolyte and electrolyte solutions of interest for a _W inhibition of microorganisms, has been calculated from freezing point data and compared with a _W values measured at 25°C. It is shown that in the important range of a _W, 0.96–0.85, the error introduced by assuming that the a _W at the freezing point is the same as that at 'room' temperature, is relatively small. In the majority of cases the difference is not likely to be larger than about 0.01 a _W units.     

大豆肽对断奶小鼠肠道生长和粘膜二糖酶活性的影响

大豆蛋白经木瓜蛋白酶酶解并过层析柱后得到大豆肽,茚三酮法测定其平均肽链长度,观察了灌喂0.25ml/d生理盐水(对照组)、4、12、20mg/ml大豆肽对小鼠肠道生长和粘膜二糖酶活性的影响。结果表明:与对照组相比,灌喂0.25ml浓度为12mg/ml的大豆肽可显著提高小鼠的体增重和小肠粘膜蛋白质含量(p<0.05),但对小肠长度和重量没有显著影响。灌喂0.25ml浓度为12和20mg/ml的大豆肽都极显著降低小鼠小肠粘膜麦芽糖酶和蔗糖酶的活性(p<0.01)。     

Mass transfer properties of osmotic solutions. II. Diffusivities

Abstract

Mass transport properties of osmotic solutions are important in controlling osmotic dehydration process. In the first paper of the series “Mass Transfer Properties of Osmotic Solutions”;, data of water activities, osmotic pressure, osmosities or osmolalities and solute activities are presented. In the present paper, the literature data on diffusivities of both binary and multi‐component osmotic solutions are presented. Some aspects of measurement methodology and mass transfer modeling are also discussed.     

丝胶蛋白质溶液的动态表面吸附过程

采用Wilhelmy吊片法测定一定浓度的丝胶溶液在不同pH条件下的动态表面张力,通过数学经验公式分析动态吸附数据,从吸附模型、吸附分子面积和吸附速率等方面,说明丝胶溶液的动态表面吸附有扩散和动力学吸附2个过程。在不同pH条件下,以丝胶溶液的动态表面压p对吸附时间t,动态表面张力tγ对lgt,以及ln(dp/dt)对p作图,根据经验公式推导出丝胶溶液表面张力下降一半时的时间t1/2、丝胶蛋白质分子吸附控制参数n,丝胶分子在界面上初始渗透和固定时所占面积ΔA1、以及在界面上重排和再取向时所占面积ΔA2。结果表明:丝胶蛋白质分子的吸附过程是扩散动态吸附;在表面上吸附的丝胶蛋白质分子的构象转变存在2个动态过程,即在界面上的分子发生初始渗透和固定阶段,以及吸附在表面上的分子发生重排和再取向阶段;丝胶溶液的pH值影响动态表面张力和分子吸附面积;在pH值低于丝胶等电点时,丝胶分子在界面初始吸附和重排面积较小,动态表面张力较高,表面吸附速度较慢,当pH值高于等电点,表面张力变小,吸附速度加快,丝胶在界面吸附的分子面积变大。     

SORPTION ISOTHERMS OF TURKISH DELIGHT

Moisture sorption isotherms of Turkish delight were determined using the gravimetric static method of saturated salt solutions at 10, 20 and 30C. Isotherms were found to be of type III, typical of high sugar foods. The effect of temperature on moisture content was not significant (P>0.05). The sorption isotherms exhibited hysteresis at low water activities (a_w < 0.5). At higher water activities the moisture content increased sharply as the temperature was increased, resulting in crossing of the isotherm curves at 0.65 water activity. Six models namely the BET, the GAB, the Halsey, the Henderson, the Chung & Pfost and the Iglesias & Chirife were evaluated to determine the best fit for the experimental data. The GAB and the Iglesias & Chirife models fitted well the data of Turkish delight in the temperature and water activity range investigated. However, the GAB model was not appropriate for the estimation of monolayer value. The Clausius-Clapeyron equation was used to examine the isosteric heats of sorption.     

Effect of stirring in the osmotic dehydration of chestnut using glycerol solutions

The use of osmotic dehydration like a previous step to drying process could be an interesting option in order to reduce costs or to preserve the characteristics of food material. This work studies the osmotic dehydration operation of chestnuts (Castanea sativa M.) with aqueous solutions of glycerol (25, 35, 45 and 60 g/100 g) and glycerol and salt (35 and 9.7 g/100 g, respectively), at different soaking times (1, 2, 4 and 8 h) at 20 °C. In order to evaluate the hydrodynamic effect of osmotic medium on the mass transfer rate, static and dynamic conditions have been tested (0, 40 and 110 rpm). The process was monitored employing several parameters related to moisture content and solid gain changes.Water loss rate using binary solutions increases with glycerol concentration and no dependency was detected with stirring level using glycerol concentration higher than 35 g/100 g. WL/SG ratio increases with glycerol concentration and linear behaviour between WL/SG and water activity of solution was established. NMC contents decrease with glycerol concentration up to 0.78 at 8 h of osmotic dehydration and NSC contents increase with glycerol concentration up to 1.12.WL kinetics using ternary solutions composed by glycerol and sodium chloride solutions were similar to the obtained with glycerol solutions at the same water activity range, but SG kinetics is improved by the acquisition of sodium chloride by the chestnut. In this way, the WL/SG ratio and NMC are lower.Model proposed by Peleg was satisfactorily employed to fit the experimental NMC and NSC data for both binary and ternary solutions considering that equilibrium value is no dependent on stirring level.